In a satellite communication system, as a method of reducing unavailability of a down feeder link due to the influence of a rainfall or the like, there are technologies disclosed in Non Patent Literature 1, Patent Literature 1, and the like. A feeder link is a line between a communication satellite and a ground base station. The down feeder link is a line in a direction of transmission from the communication satellite to the ground base station.
Non Patent Literature 1 discloses a satellite communication system including an auxiliary ground base station and using selective transmission diversity for switching a ground base station, to which a communication satellite is connected, according to a state of a propagation path to thereby reduce unavailability of a down feeder link. Patent Literature 1 discloses a technology for realizing site diversity without using a leased line. The site diversity is a technology in which a communication satellite transmits the same signal to a plurality of ground base stations to thereby reduce unavailability of a down feeder link.